Downhole energy harvesting

Abstract

Downhole electrical energy harvesting and communication in systems for well installations having metallic structure carrying electric current, for example CP current. In some instances there is a harvesting module (4) electrically connected to the metallic structure (2) at a first location and to a second location spaced from the first location, the first and second locations being chosen such that, in use, there is a potential difference therebetween due to the electric current flowing in the structure (2); and the harvesting module (4) being arranged to harvest electrical energy from the electric current. In addition or alternatively, there may be communication apparatus (4, 5, 6) for communication by modulation of the current, for example CP current, in the metallic structure (2).

The invention claimed is: 
     
       1. A downhole electrical energy harvesting system for harvesting electrical energy in a well installation having metallic structure provided with cathodic protection, the system comprising:
 a harvesting module electrically connected to the metallic structure at a first location and to a second location spaced from the first location, the first and second locations being chosen such that, in use, there is a potential difference therebetween due to the cathodic protection currents flowing in the structure; and 
 the harvesting module being arranged to harvest electrical energy from the cathodic protection currents, wherein the potential difference between the connection at the first location and the connection at the second location is less than 1 volt. 
 
     
     
       2. A downhole electrical energy harvesting system according to  claim 1  wherein the harvesting module is arranged to harvest electrical energy from dc currents. 
     
     
       3. A downhole electrical energy harvesting system according to  claim 1  wherein the current flow within portions of the metallic structure in regions between the first location and second location is in the same longitudinal direction. 
     
     
       4. A downhole electrical energy harvesting system according to  claim 1  wherein there is an uninterrupted current flow path between the first location and the second location which is at least partly via the metallic structure. 
     
     
       5. A downhole electrical energy harvesting system according to  claim 1  wherein the harvesting module is electrically connected to the metallic structure at the second location. 
     
     
       6. A downhole electrical energy harvesting system according to  claim 1  in which the spaced locations are axially spaced. 
     
     
       7. A downhole electrical energy harvesting system according to  claim 1  in which the spaced locations are radially spaced. 
     
     
       8. A downhole electrical energy harvesting system according to  claim 1  wherein at least one connection of the electrical connections between the metallic structure and the harvesting module is provided by an insulated cable. 
     
     
       9. A downhole electrical energy harvesting system according to  claim 8 , wherein the insulated cable has a conductive area of at least 10 mm{circumflex over ( )}2. 
     
     
       10. A downhole electrical energy harvesting system according to  claim 8  wherein the cable is a tubing encapsulated conductor. 
     
     
       11. A downhole electrical energy harvesting system according to  claim 1  in which the spacing between the locations is at least 100 m. 
     
     
       12. A downhole electrical energy harvesting system according to  claim 1  in which the connections are made to a common run of metallic elongate members which is part of the metallic structure. 
     
     
       13. A downhole electrical energy harvesting system according to  claim 1  in which a first of the connections is made to a first run of metallic elongate members which is part of the metallic structure and a second of the connections is made to a second, distinct, run of metallic elongate members which is part of the metallic structure. 
     
     
       14. A downhole electrical energy harvesting system according to  claim 13  wherein insulation means is provided for electrically insulating the first run of metallic elongate members from the second run of metallic elongate members in the region of the connections. 
     
     
       15. A downhole electrical energy harvesting system according to  claim 14  in which the insulation means comprises an insulation layer or coating provided on at least one of the runs of metallic elongate members. 
     
     
       16. A downhole electrical energy harvesting system according to  claim 14  in which the insulation means comprises at least one insulating centraliser for holding the runs of metallic elongate members apart from one another. 
     
     
       17. A downhole electrical energy harvesting system according to  claim 14  in which the insulation means are provided to avoid electrical contact between the two runs of metallic elongate members for a distance of at least 100 m. 
     
     
       18. A downhole electrical energy harvesting system according to  claim 1 , wherein the current flowing in the elongate members is supplied from a surface of the well. 
     
     
       19. A downhole electrical energy harvesting system according to  claim 1 , wherein the current flowing in the elongate member is supplied from one or more sacrificial anodes. 
     
     
       20. A downhole electrical energy harvesting system according to  claim 18 , wherein the current flowing in the elongate members is an impressed current from an external power supply. 
     
     
       21. A downhole electrical energy harvesting system according to  claim 1 , wherein a voltage of a surface of the well is, in use, limited to the range minus 0.7 volts to minus 2 volts with respect to a silver/silver chloride reference cell. 
     
     
       22. A downhole electrical energy harvesting system according to  claim 1  wherein resistance of the metallic structure between the electrical connections to the metallic structure at the first location and the second location is less than 0.1 ohms. 
     
     
       23. A downhole electrical energy harvesting system according to  claim 1  wherein the upper of the electrical connections to the metallic structure at the first location and the second location is:
 when the well is a land well, within 100 m of the land surface; and 
 where the well is a subsea well, within 100 m of the mudline. 
 
     
     
       24. A downhole electrical energy harvesting system according to  claim 1  wherein the upper of the electrical connections to the metallic structure at the first location and the second location is located adjacent to a location which corresponds to a maxima in magnitude of potential caused by the electric current flowing in the structure. 
     
     
       25. A downhole electrical energy harvesting system according to  claim 1  further comprising downhole communication means for transmitting and/or receiving data. 
     
     
       26. A downhole electrical energy harvesting system according to  claim 25  in which the downhole communication means is arranged for transmitting data by varying the load seen between the connections at the spaced locations. 
     
     
       27. A downhole device operation system comprising a downhole electrical energy harvesting system according to  claim 1  and a downhole device, the harvesting module being electrically connected to and arranged for providing power to the downhole device. 
     
     
       28. A downhole device operation system according to  claim 27 , wherein the downhole device comprises at least one of:
 a downhole sensor; 
 a downhole actuator; 
 an annular sealing device; 
 a valve; 
 a downhole communication module. 
 
     
     
       29. A downhole device operation system according to  claim 28  wherein the downhole device comprises a downhole sensor which comprises a pressure sensor arranged for monitoring a reservoir pressure of the well. 
     
     
       30. A downhole device operation system according to  claim 28  wherein the downhole device comprises a downhole sensor which comprises a pressure sensor arranged for monitoring the pressure in an annulus of the well. 
     
     
       31. A downhole device operation system according to  claim 28  wherein the downhole device comprises a downhole sensor which comprises a pressure sensor arranged for monitoring the pressure in an enclosed annulus of the well. 
     
     
       32. A downhole device operation system according to  claim 28 , wherein the downhole device comprises a valve and the valve comprises at least one of:
 a subsurface safety valve; 
 a bore flow control valve; 
 a bore to annulus valve; 
 an annulus to annulus valve; 
 a bore to pressure compensation chamber valve; 
 an annulus to pressure compensation chamber valve; 
 a through packer or packer bypass valve. 
 
     
     
       33. A downhole device operation system according to  claim 27  in which the downhole device is provided at a different location in the well than the harvesting module. 
     
     
       34. A downhole device operation system according to  claim 33  in which the harvesting module is disposed at a selected location downhole for harvesting power and a cable is provided for supplying electrical power further downhole to the downhole device at a different location in the well. 
     
     
       35. A downhole device operation system according to  claim 34  wherein a cross sectional area of a conductive core, or cores, of the cable used to supply the electrical power further downhole is smaller than that of cable used to connect the harvesting module to the downhole structure for harvesting the power. 
     
     
       36. A downhole electrical energy harvesting system for harvesting electrical energy in a well installation having metallic structure provided with cathodic protection, the system comprising:
 a harvesting module electrically connected to the metallic structure at a first location and to a second location spaced from the first location, the first and second locations being chosen such that, in use, there is a potential difference therebetween due to the cathodic protection currents flowing in the structure; and 
 the harvesting module being arranged to harvest electrical energy from the cathodic protection currents, wherein the voltage of the surface of the well is, in use, limited to the range minus 0.7 volts to minus 2 volts with respect to a silver/silver chloride reference cell. 
 
     
     
       37. A downhole electrical energy harvesting system for harvesting electrical energy in a well installation having metallic structure provided with cathodic protection, the system comprising:
 a harvesting module electrically connected to the metallic structure at a first location and to a second location spaced from the first location, the first and second locations being chosen such that, in use, there is a potential difference therebetween due to the cathodic protection currents flowing in the structure; and 
 the harvesting module being arranged to harvest electrical energy from the cathodic protection currents, wherein the resistance of the well structure between the first location and the second location is less than 0.1 ohms. 
 
     
     
       38. A downhole electrical energy harvesting system for harvesting electrical energy in a well installation having metallic structure provided with cathodic protection, the system comprising:
 a harvesting module electrically connected to the metallic structure at a first location and to a second location spaced from the first location, the first and second locations being chosen such that, in use, there is a potential difference therebetween due to the cathodic protection currents flowing in the structure; and 
 the harvesting module being arranged to harvest electrical energy from the cathodic protection currents, wherein the uppermost of the first location and the second location is located adjacent to a location which corresponds to a maxima in magnitude of potential caused by the electric current flowing in the structure. 
 
     
     
       39. A downhole device operation system comprising:
 i) a downhole electrical energy harvesting system for harvesting electrical energy in a well installation having metallic structure provided with cathodic protection, the downhole electrical energy harvesting system comprising: 
 a harvesting module electrically connected to the metallic structure at a first location and to a second location spaced from the first location, the first and second locations being chosen such that, in use, there is a potential difference therebetween due to the cathodic protection currents flowing in the structure, the connection to at least one of the first location and the second location being via at least one pick up cable; and 
 the harvesting module being arranged to harvest electrical energy from the cathodic protection currents; and
 ii) a downhole device provided at a different location in the well than the harvesting module, 
 
 wherein the harvesting module is: 
 electrically connected to and arranged for providing power to the downhole device, and 
 disposed at a selected location downhole for harvesting power and a power supply cable is provided for supplying electrical power further downhole to the downhole device, wherein the cross sectional area of the conductive core, or cores, of the power supply cable used to supply the electrical power further downhole is smaller than that of the at least one pick up cable. 
 
     
     
       40. A downhole electrical energy harvesting system for harvesting electrical energy from dc currents in a well installation having metallic structure, the metallic structure being provided with cathodic protection and comprising at least one run of downhole metallic pipe and, the system comprising:
 a harvesting module electrically connected to the at least one run of downhole metallic pipe of the metallic structure at a first location and electrically connected to the at least one run of downhole metallic pipe of the metallic structure at a second location spaced from the first location, the first and second locations being chosen such that, in use, cathodic protection currents flow in the at least one run of downhole metallic pipe between the first and the second location such that there is a potential difference between the first and second locations due to the cathodic protection currents flowing in the at least one run of downhole metallic pipe; and 
 the harvesting module being arranged to harvest electrical energy from dc currents, being connected between the first and second locations and being arranged to harvest electrical energy due to the potential difference which exists between the first and second locations due to the cathodic protection currents flowing in the at least one run of downhole metallic pipe. 
 
     
     
       41. A downhole electrical energy harvesting system according to  claim 1  wherein the harvesting module is arranged to harvest electrical energy from dc currents, and wherein the harvesting module is electrically connected to the metallic structure at the second location. 
     
     
       42. A downhole electrical energy harvesting system according to  claim 1 ,
 wherein the harvesting module is arranged to harvest electrical energy from dc currents, 
 wherein the metallic structure comprises at least one run of downhole metallic pipe and the harvesting module is electrically connected to the at least one run of downhole metallic pipe of the metallic structure at the first location and is electrically connected to the at least one run of downhole metallic pipe of the metallic structure at the second location, 
 wherein the first and second locations are chosen such that, in use, cathodic protection currents flow in the at least one run of downhole metallic pipe between the first and the second location such that there is a potential difference between the first and second locations due to the cathodic protection currents flowing in the at least one run of downhole metallic pipe; and 
 the harvesting module is arranged to harvest electrical energy from dc currents and is connected between the first and second locations and arranged to harvest electrical energy due to the potential difference which exists between the first and second locations due to the cathodic protection currents flowing in the at least one run of downhole metallic pipe.